Mapping the future: new pathways for greenhouse gas concentrations

09/26/2011 - Behind grand projections of global warming’s impacts and recommendations for mitigation, there is huge not-so-glamourous research. Four new benchmark scenarios for future climate change are being presented now, ranging from – for the first time – a low emission scenario assuming ambitious mitigation action, which would keep temperature rise below 2 degrees Celsius, to a very high scenario. These so-called Representative Concentration Pathways, also for the first time, have been extended to the year 2300. This is more than just an update of the previously used scenarios.

Coal-fired power plant. Photo: thinkstock

All this will be the basis for the next report of the U.N.’s Intergovernmental Panel on Climate Change (IPCC) in 2013/14, mapping the future so that the pathways are the common reference for the global scientific community. Scientists of the Potsdam Institute for Climate Impact Research (PIK) are at the heart of this process, which involves many international partners.

“Staying below the threshold of 2 degrees is still possible, but it is a close call,” says Malte Meinshausen of PIK. He is one of the authors of a special issue of the journal Climatic Change focusing on the scenario development that is to be published in November. The new low emission scenario is expected to shed light on ambitious mitigation options and unavoidable adaptation needs – “this is something that has been lacking before”. Such systematic research across the scientific community has so far only been done for no-climate-policy worlds. Limiting global warming to below 2 degrees Celsius above pre-industrial levels is considered to give a good chance to prevent dangerous climate change. However, humankind would have to let peak emissions “before 2020,” Meinshausen says.

“Changing your mind mid-course is hardly an option”

One result of this scenario work is that “changing your mind mid-course is hardly an option,” Meinshausen says. After first following a high scenario until one considers climate change impacts too high towards the end of the century, and then attempting to aim for a climate that would have resulted from a low mitigation scenario instead, “seems technologically challenging to the degree that it can be judged impossible”. Thus it is important of which trajectory decision-makers choose to embark on.

As such, scenarios help to explore the implications of climate policy or climate inaction by informing about different possible futures. They consist of large sets of data – ranging from land use patterns to gridded tropospheric ozone precursor emissions – and assumptions on the complex interplay of physical and chemical processes. PIK’s contribution in this collaborative exercise within the scientific community was to turn the underlying emission scenarios into the benchmark set of greenhouse gas concentrations from pre-industrial times to 2300. The latest knowledge on the Earth system’s response to anthropogenic emissions was synthesized in order to arrive at this best-estimate benchmark which is going to be used as the very basis for ongoing climate model intercomparisons.

Socio-economic scenarios are an important complement

Complementary to this are the socio-economic scenarios. "People and businesses obviously are drivers of climate change," says Elmar Kriegler of PIK. "At the same time, they are affected by the impacts of global warming." Both the magnitude of their contribution to greenhouse gas emissions from burning fossil energy and their ability to adapt to impacts, such as sea level rise, depend on factors like population growth and wealth. This is why another large international team of researchers, including Kriegler, is working on a new common framework for these socio-economic scenarios. It will be completed in November. In the end there will be a matrix combining different socio-economic scenarios with emission scenarios (the Representative Concentration Pathways).

"Together, they provide the basis not just for sound research on climate change,” says Kriegler. "The results thereof should enable an integrated assessment of climate mitigation, adaptation and residual impacts across a wide range of plausible futures.”